1. Field Of The Invention
This invention relates to 8-hydroxyquinoline substituted with an alpha-alkenyl group on the non-hetero ring and to a process for the preparation of such derivatives.
2. Description Of The Prior Art
The compound 8-hydroxyquinoline is well known for its ability to coordinate with ions of a variety of transition metals through covalent bonding to form a relatively stable 5-membered ring which complexes are commonly referred to as metal chelates. This complexing technique has been used extensively heretofore in chemical analytical procedures. Recently, however, the ability of the 8-hydroxy quinoline configuration to form chelates with the transition metals has been utilized in hydrometallurgical extraction processes applicable for the recovery of such metal values from aqueous solutions thereof. These extraction processes comprise basically a two step operation. In the first step an impure aqueous phase containing the desired metal values in ionic form is intimately contacted with a water-immiscible organic solution of the metal collector to facilitate an interfacial relationship of the phases whereby the metal ions are readily and preferentially extracted into the organic phase in the form of a chelate. The second step, which is referred to as stripping, serves to regenerate the extracted metal values in ionic form and to effect the transfer thereof to an aqueous phase thus resulting in a pure and relatively concentrated solution of the desired metal from whence it can then be readily recovered such as by an electrolytic process.
Unfortunately, 8-hydroxyquinoline itself cannot be effectively used in the aforedescribed extraction processes because it is not sufficiently soluble in the hydrocarbon solvents employed to provide the organic phase and whereas it is too soluble in the acidic aqueous stripping phases. The deficiencies of 8-hydroxyquinoline in this regard can be overcome, however, by providing a bulky hydrocarbyl substituent thereon which, if properly chosen as to carbon atom content, will markedly enhance its oil-solubility characteristics; and at the same time reduce its solubility even in strong acidic aqueous mediums to essentially a nil value. It is also known that the molecular configuration of such a substituent is important from the standpoint of increasing the loading capabilities of the base compound.
A class of 8-hydroxyquinolines modified in the foregoing manner is exemplified in U.S. Pat. No. 3,637,711. These substituted 8-hydroxyquinolines are characterized in having a higher B-alkenyl group in the No. 7 position. The foregoing compounds have proven to be excellent collectors and can be effectively used in all types of metal extraction processes including those which require a pH range as low as 1-2. The only disadvantage of these prior art extractants is that their method of preparation calls for the use of a higher allylic chloride which is a difficult and thus a relatively expensive reagent to manufacture. Accordingly, the foremost objective of the present invention is to provide similarly functional 8-hydroxyquinoline derivatives as those of the aforementioned patent but which are substantially more economical to synthesize. SUMMARY OF THE INVENTION
In accordance with this invention a class of alpha alkenyl substituted 8-quinolinols are provided corresponding to the following structural formula: ##STR1## wherein R and R' represent alkyl groups having a sum total of from 6 to 18 carbon atoms.
In a further aspect, a process is provided for preparing the aforesaid compounds which comprises reacting 8-quinolinol with a branched secondary aldehyde having the formula: ##STR2## wherein R and R' have the above-mentioned meanings. The foregoing process is carried out at an elevated temperature and under conditions facilitating the removal of water of dehydration ensuing upon, or concominantly generated in effecting the condensation of the aldehyde and the quinolinol.